What is it about the faces on these pages that we find so intriguing? Is it simply that their features disrupt our expectations, that we’re not used to seeing those eyes with that hair, that nose above those lips? Our responses can range from the armchair anthropologist’s benign desire to unravel ancestries and find common ground to active revulsion at group boundaries being violated or, in the language of racist days past, “watered down.”

Out in the world, the more curious (or less polite) among us might approach, asking, “Where are you from?” or “What are you?” We look and wonder because what we see—and our curiosity—speaks volumes about our country’s past, its present, and the promise and peril of its future.

The U.S. Census Bureau has collected detailed data on multiracial people only since 2000, when it first allowed respondents to check off more than one race, and 6.8 million people chose to do so. Ten years later that number jumped by 32 percent, making it one of the fastest growing categories. The multiple-race option has been lauded as progress by individuals frustrated by the limitations of the racial categories established in the late 18th century by German scientist Johann Friedrich Blumenbach, who divided humans into five “natural varieties” of red, yellow, brown, black, and white. Although the multiple-race option is still rooted in that taxonomy, it introduces the factor of self-determination. It’s a step toward fixing a categorization system that, paradoxically, is both erroneous (since geneticists have demonstrated that race is biologically not a reality) and essential (since living with race and racism is). The tracking of race is used both to enforce antidiscrimination laws and to identify health issues specific to certain populations.

The Census Bureau is aware that its racial categories are flawed instruments, disavowing any intention “to define race biologically, anthropologically, or genetically.” And indeed, for most multiple-race Americans, including the people pictured here, identity is a highly nuanced concept, influenced by politics, religion, history, and geography, as well as by how the person believes the answer will be used. “I just say I’m brown,” McKenzi McPherson, 9, says. “And I think, Why do you want to know?” Maximillian Sugiura, 29, says he responds with whatever ethnicity provides a situational advantage. Loyalties figure in too, especially when one’s heritage doesn’t show up in phenotypical facial features, hair, or skin. Yudah Holman, 29, self-identifies as half Thai and half black, but marks Asian on forms and always puts Thai first, “because my mother raised me, so I’m really proud of being Thai.”

Sandra Williams, 46, grew up at a time when the nation still turned on a black-white axis. The 1960 census depicted a country that was still 99 percent black or white, and when Williams was born six years later to parents of mixed black and white ancestry, 17 states still had laws against interracial marriage. In Williams’s western Virginia hometown, there was only one Asian child in her school. To link her own fair skin and hair to her white ancestry, Williams says, would have been seen by blacks as a rejection. And so, though she views race as a social construction, she checks black on the census. “It’s what my parents checked,” she says.

In today’s presumably more accepting world, people with complex cultural and racial origins become more fluid and playful with what they call themselves. On playgrounds and college campuses, you’ll find such homespun terms as Blackanese, Filatino, Chicanese, and Korgentinian. When Joshua Ahsoak, 34, attended college, his heritage of Inupiat (Eskimo) and midwestern Jewish earned him the moniker Juskimo, a term he still uses to describe himself (a practicing Jew who breaks kosher dietary laws not for bacon but for walrus and seal meat).

Tracey Williams Bautista says her seven-year-old son, Yoel Chac Bautista, identifies himself as black when he’s with her, his African-American parent. When he’s with his father, he’ll say Mexican. “We call him a Blaxican,” she jokes, and says she and her husband are raising him in a home where Martin Luther King, Jr., is displayed next to Frida Kahlo. Black relatives warn Williams about the persistence of the one-drop rule, the long-standing practice of seeing anyone with a trace of black “blood” as black. “They say, ‘He may be half, but he’s still the N word.’”

Certainly, race still matters in this country, despite claims that the election of Barack Obama heralded a post-racial world. We may be a pluralist nation by 2060, when the Census Bureau predicts that non-Hispanic whites will no longer be the majority. But head counts don’t guarantee opportunity or wipe out the legacy of Japanese-American internment camps or Jim Crow laws. Whites, on average, have twice the income and six times the wealth of blacks and Hispanics, and young black men are twice as likely as whites to be unemployed. Racial bias still figures into incarceration rates, health outcomes, and national news: A recent Cheerios commercial featuring an interracial family prompted a barrage of negative responses, including claims of white genocide and calls for “DIEversity.”

Both champions and detractors of that ad based their views on what’s known as the eyeball test: A study of brain activity at the University of Colorado at Boulder showed that subjects register race in about one-tenth of a second, even before they discern gender. In May researchers reported that political conservatives are more likely than liberals to categorize ambiguous black-white faces as black. We assign meaning in the blink of an eye.

When people ask Celeste Seda, 26, what she is, she likes to let them guess before she explains her Dominican-Korean background. She points out that even then she has revealed only a fraction of her identity, which includes a Long Island childhood, a Puerto Rican adoptive family, an African-American sister, and a nascent acting career. The attention she gets for her unusual looks can be both flattering and exhausting. “It’s a gift and a curse,” Seda says.

It’s also, for the rest of us, an opportunity. If we can’t slot people into familiar categories, perhaps we’ll be forced to reconsider existing definitions of race and identity, presumptions about who is us and who is them. Perhaps we’ll all end up less parsimonious about who we feel connected to as we increasingly come across people like Seda, whose faces seem to speak that resounding line from Walt Whitman’s “Song of Myself”: